Electrochemical stability and lithium ion-anion interactions of orthoborate anions (BOB, MOB, BMB), and presentation of a novel anion: Tris-oxalato- phosphate

Abstract

Ab initio calculations reveal the extraordinary low lithium ion affinities of the orthoborate anions bis(oxalate)borate (BOB), malonato-oxalatoborate (MOB), and bis(malonato)borate (BMB). HF and MP2 calculations reveal these anions to be less prone to associate with Li+ (by ∼10%) than most anions used today, e.g., PF6-, BF4-, and TFSI, in low dielectric media such as polymeric electrolytes. Furthermore, by using self-consistent reaction field calculations to model the effect of high dielectric solvents present, the applicability of these anions also for liquid and gel electrolytes was proven. Future directions of lithium salt synthesis are outlined and exemplified by a new anion, suggested here for the first time. The HOMO levels of the anions are correlated to electrochemical stabilities in electrolytic solutions; all studied anions can be anticipated to have wide stability ranges. Finally, a new methodology to obtain starting data for geometry optimizations of cation-anion pairs by global optimization is presented. © 2005 The Electrochemical Society. All rights reserved.